Ive got a 1999 and have been having some idle issues lately. My pops is familiar with the vehicle, and as am I but the problem wasn't resolved after we both went through it.

Issue is as follows:

Low idle leading to stall out. Between 500 and 1000 RPM, the motor will struggle to maintain stability, and hard idle to near stall out unless gassed to 2k RPM to bring idle back to 1k RPM. Inital thought was vaccum leak, which, admittedly, some old rotted hoses were there, and replaced. However, even with replacing those hoses, issue wasnt resolved, and still occurs. Going into the situation, I've replaced both spark plugs and wires, air filter, and upper radiator hose (for context, the hose was ballooning and I had the impression that it may have had a pin hole in the line sucking air into the system) as of current date and time, I have a fuel filter and o2 sensors to throw in, along with fuel injectors coming in as well.

Outside all that, do y'all have any ideas to throw at the wall that can possible resolve this issue?

Thanks in advance

-JCS13

 

Assuming 4.0l engine
Manual or automatic?

Gasoline engines need to be Choked when cold, fuel injection doesn't change that
So on Cold Start you should get 1,000-1,200rpm idle, the colder the temp the higher the idle
This is done by the computer(PCM) using the IAC(idle air control) Valve AND the ECT(engine coolant temp) sensor
PCM has "Target idles" in memory matched to Temp of coolant(ECT)
Computer runs a Rich fuel mix until engine/coolant gets above 140degF, that's the Choke part

IAC Valve is a simple 12volt solenoid that has a spring and valve on an air passage that bypasses the Throttle Plate, looks like a can on its side
These can/do control idle RPMs +/- 4rpm so very acurate

On cold start if you don't get 1,000+ rpms then there is a problem with ECT or IAC Valve
If you have or can get an OBD2 reader you can see what ECT shows before cold start, should be outside temp, if its showing 150degF then no choke and engine would struggle to run

After engine is warm up and idling, unplug the 2 wire connector on the IAC Valve, RPMs should drop to 500-600, engine may even stall, but either means the IAC Valve was OPEN at least a bit
If idle doesn't change then IAC valve is not working
With key on engine off use a Volt meter on the unplugged IAC Valve's wires, should see 11-12volts, if not computer is not working for IAC Valve or a wire is broken

You can ONLY use Motorcraft or Hitachi IAC Valves on these Rangers, other brands will not work well


If you have an automatic shift to Neutral when engine starts to stall, could be TCC solenoid is not releasing the torque converter which causes engine to stall